> The issue is that the error production cannot create a meaningful node> so what actions to replace ACTION are appropriate? Here are some> options.>> * Create an X node with dummy values. That would satisfy the type> checking.> * Set $<err_msg>$ = "invalid X node"> * Braces but no action, i.e. {}> * No action clause so default to $$ = $1;> * Some combination of YYERROR; and yyerror();